An extensive flow cytometric evaluation continues of patients with autoimmune lymphoproliferative syndrome (ALPS) and their extended family members, on the basis of characterization of the expanded double-negative T-cell and B-cell populations. Double-negative T-cells have been demonstrated to be alpha beta TcR, CD57+, HLA-DR+, and CD45RA+. This study has been extended to characterize the double-negative T-cells more completely including B220 expression and gamma-delta TcR T-cells in all ALPS patients. In addition, we have initiated expanded characterization of the B cells, directed at memory B cells using CD27 and B220 assessment in these patients. More recently, we have identified a relative deficiency in CD4/CD25 T cells that could be associated with the autoimmunity in this disorder based on recent information identifying this T cell as a critical immunoregulatory T cell. Functional studies directed at this T cell subpopulation will be initiated in the near future.